For training purposes it is desirable that trainees use the same weapon they would use in actual combat. However, it is also desirable that they use smaller caliber ammunition if possible. In the case of an infantry rifle, for example, if .22 caliber cartridges could be used instead of standard 5.56mm ammunition, the cost of the smaller training ammunition would be only 10% of that for which the rifle was designed. To achieve this 90% saving, rim fire adapter assemblies have been developed which replace the standard bolt and magazine assemblies in the rifle. One such magazine and bolt adapter is disclosed in copending application Ser. No. 617,203, filed Sept. 26, 1975, and entitled Rifle Adapter Assembly in which Applicant is a Co-inventor. In that invention bolt travel on recoil was such that the bolt caused the hammer to cock before the bolt chambered the next cartridge from the magazine. This prevented a safety hazard known as doubling.
All known commercially available rimfire adapters share this common safety hazard of having a potential for doubling, that is, firing two cartridges upon the squeeze of the trigger. During recoil, the feed position of the bolt for chambering the next round is reached before the hammer is cocked. Consequently, a short recoil can cause the empty case to be extracted and ejected, and a live round to be fed into the chamber, whereupon the uncocked hammer will follow the bolt into battery, firing the live cartridge. Thus, two cartridges will have been fired with one pull of the trigger. Repetition of this malfunction can result in several cartridges being fired with one trigger pull.